"Our field records will be perhaps the most valuable of all our results. You can't tell in advance which observations will prove valuable. Do record them all!"

- Joseph Grinnell, UC Berkeley, Museum of Vertebrate Zoology, 1908

YOSEMITE NATIONAL PARK – High above a silver-blue mountain lake, a gray-bearded man tromped up a rocky slope and peered at a small metal trap. It was empty.

He kept moving, scrambling across huge granite boulders and found another trap. This time, success: "We got something," he said.

Jim Patton, a retired professor of zoology at UC Berkeley, had his quarry: the tiny ash-gray alpine chipmunk, a Sierra Nevada native that is now one of the leading sentinels – and apparent victims – of climate change in the United States.

One century ago, alpine chipmunks owned the upper half of Yosemite. They skittered under logs and darted across rocks from the rugged Sierra crest down to the conifer forests at 7,800 feet. Today, they are missing in action below 9,800 feet.

"It's lost half its geographic range," Patton said. "Climate is the culprit. I don't think there is any iota of reason not to think that."

Tipping the box-like trap, Patton shook it and one very frightened chipmunk tumbled out into a white sack. Patton gently snipped a piece of flesh from its ear for a DNA sample – and released it. Next he pulled out a notebook and wrote down the elevation: 10,020 feet. Seven hundred feet overhead, the slope he was working on yielded to blue sky. "Eventually, it's going to get shoved off these mountains and go extinct," Patton said.

For years, climate change was a story told largely via melting snow and ice. Now, species and ecosystems are feeling the heat, too. Butterflies are expanding their ranges northward. Migratory birds are arriving earlier in the spring. And here in the Sierra and in other mountain ranges around the world, species not considered migratory at all – from stately conifers to diminutive chipmunks – are on the move, creeping upslope toward cooler, more hospitable abodes.

Along with that movement comes stress and danger. Ultimately, national parks such as Yosemite could lose significant portions of their mammal species as habitats unravel due to climate warming from the buildup of greenhouse gases, according to a 2003 paper published by the National Academy of Sciences.

"Animals that can fly are in pretty good shape," said David Graber, chief scientist for the National Park Service in California. "Animals that are relatively static have a much more limited ability to move. If climate changes faster than they can find new habitat, they're out of business."

About the size of your cell phone, the alpine chipmunk may not be a well-known symbol of climate change. It's hard to compete, after all, with a 600-pound polar bear stranded on melting slabs of sea ice. But the drama unfolding here along the roof-beam of the Sierra is just as poignant and populated by a cast of unsung creatures – from ground squirrels to wood rats – that are at risk, as well.

It is a story that might have remained untold if not for the pioneering work of Joseph Grinnell, the founding director of UC Berkeley's Museum of Vertebrate Zoology who directed the first in-depth survey of Yosemite's wildlife almost a century ago.

An eye for detail

Seeking specimens for his new museum, Grinnell set out across the park with a team of assistants for one of his expeditions in the summer of 1915. They trapped ground squirrels, shot songbirds and even bagged a wolverine. But unlike other collectors, they took elaborate notes on everything – whether they captured it or not. Grinnell was the note taker in chief.

"We'd be sitting in camp and we'd both be skinning. Pretty soon, he'd throw a rat over to me and he'd say: 'Here, Russell, finish this one up' and he'd just … pick up his notebook and start writing," one colleague, Ward Russell, said about Grinnell in an interview with a UC Berkeley professor in 1992 (listen to it online at www.sacbee.com/links).

Call The Bee's Tom Knudson, (530) 582-5336.